Re: draft-baker-6man-multiprefix-default-route-00.txt is a newdraft

Iljitsch van Beijnum writes:
> On 13 nov 2007, at 13:46, James Carlson wrote:
> works. (Such as the shim6 REAP protocol is designed to do although  
> REAP doesn't know about routes.) So it should clearly be possible to  
> send packets that don't conform to the source address / route  
> alignment. However, having this alignment by default would be good.

Yes, I agree that getting the alignment where possible is good.

> I'm not so sure that routers correcting "misbehaving" hosts here by  
> selecting a different route based on the source address is a good  
> default behavior, though, as this could make for a performance hit.

I don't think avoiding that performance hit is a possibility.  Section
2.3 of the draft discusses exactly this issue and offers forwarding at
each hop based on the source address as a resolution.  Every router
with multiple routes to a given destination will need to deal with
this.

That appears to come to the same result, at least in terms of looking
up the right answer.

The proposal seems to me to have a lot of sharp edges.  For instance,
if one of those upstream routers advertises a more specific route (not
just the default route), then forwarding will find this one route
first, even when the source address doesn't match that path, and even
when some *other* router advertising a less-specific route would be
able to forward the packet correctly.

The draft suggests that source address comes into play only when the
routes are equal -- multipath routes.  Given the likely failure modes,
I'm not sure I understand whether, why, and when the source address
ought to be given a lower weighting than the destination address.

-- 
James Carlson, Solaris Networking              <james.d.carlson@sun.com>
Sun Microsystems / 35 Network Drive        71.232W   Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757   42.496N   Fax +1 781 442 1677

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